The present invention relates to a control signal transfer device, which transfers electric ON/OFF information transmitted from a position detecting sensor to a receiving device through radio wave, to thereby control a position of a work or a machine.
Conventionally, in order to transfer electric ON/OFF information, i.e. signal, transmitted from a position detecting sensor to a control or receiving device, an electric wire is installed between the position detecting sensor and the control device. However, the electric wire may possibly be cut. Especially, in case an attaching surface of the position detection sensor is irregular or in a turret form, the electric wire may be turned or tangled. Thus, a wireless device for transmitting a signal has been utilized.
The first method in the wireless transmitting methods uses dielectric coupling. In this method, an induction coil, to which alternate current is supplied through the control device, is located adjacent to an induction coil provided in a position detecting sensor to form electromotive force. Inductance of the induction coil in the position detecting sensor is changed due to ON/OFF operation of a switch of the position detecting sensor, by which the alternate current is changed. The change of the alternate current is detected and amplified to thereby control the control device.
As the second method in the wireless transmitting methods, an infrared irradiation device, such as LED, is formed in a main body of a position detecting sensor. An ON/OFF signal outputted from the position detecting sensor is changed to electric current, which is then supplied to the infrared irradiation device to output a light signal. The light signal is received by a light receiving device situated away from the position detecting sensor, and is changed again to electric signal, which is amplified to supply control current to the control device.
As the third method in the wireless transmitting methods, an ON/OFF signal obtained from the position detecting sensor is changed to radio wave by, for example, FM modulation, which is outputted from a transmitting antenna installed on the position detecting sensor. The radio wave is received by a receiving antenna situated away from the position detecting sensor, and is detected and amplified to supply control current to the control device.
One of the wireless device is disclosed in U.S. Pat. No. 4,339,714.
In the first method, the distance between the induction coil of the position detecting sensor and the induction coil formed at the control device is very narrow, such as 1 mm. Thus, in case metal powder, such as iron powder, is filled or clogged in the gap between the two induction coils facing each other, induction rate changes to cause malfunction of the control operation.
In the second method, cutting oil or powder may attach to the irradiation device and the light receiving device, or cross a light path. As a result, light transferred to the light receiving device is reduced or completely shut off, so that control may not be made completely.
In the third method, there is no possibility of trouble by the cutting oil or cutting powder as in the first and second methods, but there is a time lag until starting the operation of an oscillation circuit for the radio wave and receiving, detecting and amplifying circuits. Thus, the problem lies in a time lag or rise time from the output of the ON/OFF signal to the operation of the control circuit.
For example, in case a transmitting speed for a cutting blade, such as bit, is 100 mm/min., it is required that the rise time for obtaining an accuracy of 1 micrometer is less than 0.6 milli-second.
Further, it is required to prevent malfunction of the control device in case there is a radio wave shielding material in a middle of the transmitting antenna and the receiving antenna. For this purpose, the output of the radio wave must be increased, and the receiving sensitivity must be raised. As a result, in case the same kind of devices are installed parallel to each other, the radio waves are interfered or mixed to cause error operation.
Therefore, it is required to solve the problems by, such as changing frequencies in each model, to thereby increase cost of the devices. Further, in case sensitivity for receiving the radio wave is raised, other radio waves may be caught by the receiving antenna, which may cause error operation.
It is therefore an object of the invention to provide a control signal transfer device for a position detecting sensor, which can prevent radio interference among the same devices as well as other radio waves by using very weak radio wave for a short distance as a transmission medium.
Another object of the invention is to provide a control signal transfer device as stated above, wherein rise time of the circuits is shortened by simplifying the circuits.
A further objects of the invention is to provide a control signal transfer device as stated above, wherein the device is economical and easy to use, and is not affected by cutting oil and cutting powders.
Further objects and advantages of the invention will be apparent from the following description of the invention.